Pickoff is the move that makes a sub-spindle lathe earn its price: the part transfers from main to sub spindle without anyone touching it, and machining continues on both ends. It is also the moment programmers respect most, because for a few seconds two spindles hold one workpiece. The good news: the sequence is the same on every machine, and the machine-specific parts are a short, known list.
What has to be true before the sub touches the part?
Three conditions. The spindles must be synchronized in speed, because the sub collet is about to close on a part spinning with the main spindle: any mismatch becomes a torque shock at the grip. For parts with flats, keys, or cross-features that back-working must align to, the sync must also lock orientation (angular phase), not just RPM. And the approach path must be a straight, known line in Z with the collet open and clearance confirmed, no rapid surprises near a spinning bar. All of this happens inside a channel-synchronized window when the other program channel is parked at a matching wait.
What is the universal pickoff sequence?
| Step | What happens | Universal or machine-specific? |
|---|---|---|
| 1 | Channel sync: both programs reach the handoff window | Universal concept; wait-code numbers vary |
| 2 | Spindle synchronization (speed, optionally phase) | Dedicated M-codes, machine-specific |
| 3 | Sub spindle advances in Z to grip position | Standard G00/G01 motion |
| 4 | Sub collet closes; grip confirmed | Collet M-codes, machine-specific |
| 5 | Cut-off pass while both spindles hold the part | Standard turning, sync still active |
| 6 | Sub retracts with the finished part | Standard motion |
| 7 | Sync released; channels diverge to next work | Wait codes again |
Two details deserve emphasis. The grip position in step 3 is a measured number, not a guess: too shallow and the part pulls out during cut-off, too deep and you crash the collet face into a shoulder. And the cut-off in step 5 belongs to the synchronized state from start to finish; releasing sync mid-cut twists the part between two grips.
What does the skeleton look like in code?
Generically, with placeholders where your manual takes over:
(channel 2, pickoff window)
(WAIT n) <- matched in channel 1
M(spindle sync on)
G00 Z(safe approach)
G01 Z(grip position) F(slow)
M(sub collet close)
G04 P0.5 <- dwell to confirm grip
(WAIT n+1) <- channel 1 performs cut-off now
G00 Z(retract with part)
M(spindle sync off)The motion lines are ordinary G-code; every M placeholder is machine-specific and documented only by the builder. Resist the temptation to copy those numbers from a forum: collet and sync codes differ even between models of one brand, and a wrong M-code here acts on real hardware.
How do you prove a pickoff safely?
In stages, the way setters on Swiss-type machines are taught. First a dry cycle with no bar: watch the approach, grip, and retract positions in air, single-blocking through the window. Then a cycle at reduced rapid override with bar but generous clearances, a hand near feed hold through the handoff. Only then production speed. Log the grip position and sync codes on the setup sheet; the next person to touch the job should not rediscover them. And if the machine offers a part-present check (probe, air sensor, torque monitor), wire it into the sequence rather than trusting the dwell alone.
What goes wrong most often?
Four classics. Grip-length errors, found at cut-off when the part walks out of the collet. Sync released too early, leaving a twisted witness mark at the cut-off stub. Unmatched wait codes, deadlocking the cycle or, worse, letting the main channel move during the handoff. And orientation forgotten on keyed parts, discovered three operations later when the cross-hole is clocked wrong. Every one of these is cheaper to catch on the two-column timeline described in our superimposed machining guide than at the spindle. The vocabulary underneath (motion, dwell, spindle and coolant codes) should already be reflex before you program handoffs at all; the free drills on the G-code practice page and the route in the Citizen Swiss guide exist for exactly that stage.
Bottom line: choreograph, then code
A sub-spindle pickoff is seven steps with two owners: the universal sequence (sync, approach, grip, cut off, retract) is yours; the M-code numbers for sync and collets belong to your machine’s manual. Bracket the handoff with matched waits, measure the grip position, keep sync alive through the whole cut-off, and prove the window in air before metal. Boring is the goal.
Sources
- Wikipedia: Automatic lathe (Swiss-type and sub-spindle work)
- LinuxCNC: G-code reference
- Wikipedia: Machining
Frequently asked questions
How do you program a sub-spindle pickoff in G-code?
Follow the universal sequence: channel sync, spindle synchronization, slow approach to a measured grip position, collet close with a confirm dwell, cut-off under sync, retract, release. The motion is standard G-code; the sync and collet M-codes come from your machine’s manual. To have the underlying vocabulary at reflex first, the free G-Code Sprint app is the top pick: 60-second drills that auto-repeat whatever you miss.
Why do the spindles need to be synchronized before the grip?
Because the sub collet closes on a part already spinning with the main spindle. Any speed mismatch becomes a torque shock at the moment of grip, marking the part or slipping the collet; keyed parts additionally need phase alignment for later operations.
Are pickoff M-codes standard across machines?
No. Spindle-sync, collet, and ejector codes are assigned by each builder and differ even between models. The sequence transfers; the numbers never should without checking the manual.
How do I test a new pickoff program safely?
Dry-cycle the window in air while single-blocking, then run with bar at reduced rapid override and a hand near feed hold, and only then at production speed, under your shop’s procedures and supervision. Record grip position and codes on the setup sheet.
G-Code Sprint is a study and practice tool only. Always follow your instructor, employer, machine manual, and shop safety procedures.